diff --git a/services/platform-service/src/modules/diagnostics/types.ts b/services/platform-service/src/modules/diagnostics/types.ts
new file mode 100644
index 00000000..c00c431b
--- /dev/null
+++ b/services/platform-service/src/modules/diagnostics/types.ts
@@ -0,0 +1,381 @@
+/**
+ * Diagnostics types — remote debug session management.
+ *
+ * Cosmos containers:
+ * - debug_sessions (pk: /id, TTL: 7 days)
+ * - debug_traces (pk: /pk composite ${productId}:${sessionId}, TTL: 7 days)
+ * - debug_logs (pk: /pk composite ${productId}:${sessionId}, TTL: 3 days)
+ * - debug_screenshots (pk: /sessionId) — metadata only, images in Azure Blob
+ *
+ * @module diagnostics
+ */
+
+import { z } from 'zod';
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Enums
+// ─────────────────────────────────────────────────────────────────────────────
+
+export const SessionStatusEnum = z.enum(['pending', 'active', 'paused', 'completed', 'cancelled']);
+export type SessionStatus = z.infer<typeof SessionStatusEnum>;
+
+export const CollectionLevelEnum = z.enum(['standard', 'debug', 'trace']);
+export type CollectionLevel = z.infer<typeof CollectionLevelEnum>;
+
+export const LogLevelEnum = z.enum(['debug', 'info', 'warn', 'error', 'fatal']);
+export type LogLevel = z.infer<typeof LogLevelEnum>;
+
+export const ScreenshotTriggerEnum = z.enum(['manual', 'error', 'interval', 'user_request']);
+export type ScreenshotTrigger = z.infer<typeof ScreenshotTriggerEnum>;
+
+export const SpanStatusEnum = z.enum(['ok', 'error', 'unset']);
+export type SpanStatus = z.infer<typeof SpanStatusEnum>;
+
+export const SpanKindEnum = z.enum(['internal', 'server', 'client', 'producer', 'consumer']);
+export type SpanKind = z.infer<typeof SpanKindEnum>;
+
+// ─────────────────────────────────────────────────────────────────────────────
+// DebugSessionDoc
+// ─────────────────────────────────────────────────────────────────────────────
+
+export interface DebugSessionDoc {
+  id: string;
+  productId: string;
+
+  // Target (at least one required)
+  targetUserId?: string;
+  targetAnonymousId?: string;
+  targetDeviceId?: string;
+  targetSessionId?: string;
+
+  // Status
+  status: SessionStatus;
+
+  // Collection config
+  collectionLevel: CollectionLevel;
+  captureLogs: boolean;
+  captureNetwork: boolean;
+  captureScreenshots: boolean;
+  screenshotOnError: boolean;
+  maxDurationMinutes: number;
+
+  // Timestamps
+  createdAt: string;
+  updatedAt: string;
+  startedAt?: string;
+  endedAt?: string;
+  expiresAt: string;
+
+  // Stats (denormalized)
+  logCount: number;
+  traceCount: number;
+  screenshotCount: number;
+
+  // Audit
+  createdBy: string;
+  updatedBy?: string;
+
+  // Consent tracking
+  userConsent?: {
+    consentedAt: string;
+    consentMethod: 'prompt' | 'pre_consent' | 'auto';
+  };
+}
+
+// ─────────────────────────────────────────────────────────────────────────────
+// DebugTraceDoc (OpenTelemetry-compatible)
+// ─────────────────────────────────────────────────────────────────────────────
+
+export interface DebugTraceDoc {
+  id: string;
+  pk: string; // Composite: ${productId}:${sessionId}
+  sessionId: string;
+  productId: string;
+
+  // OTel context
+  traceId: string;
+  parentId?: string;
+  spanId: string;
+  name: string;
+  kind?: SpanKind;
+
+  // Timing
+  startTime: string;
+  endTime?: string;
+  durationMs?: number;
+
+  // Context
+  attributes: Record<string, unknown>;
+  status: SpanStatus;
+  statusMessage?: string;
+
+  // Events within span
+  events?: Array<{
+    name: string;
+    timestamp: string;
+    attributes?: Record<string, unknown>;
+  }>;
+
+  // Links to other traces
+  links?: Array<{
+    traceId: string;
+    spanId: string;
+    attributes?: Record<string, unknown>;
+  }>;
+}
+
+// ─────────────────────────────────────────────────────────────────────────────
+// DebugLogEntryDoc
+// ─────────────────────────────────────────────────────────────────────────────
+
+export interface DebugLogEntryDoc {
+  id: string;
+  pk: string; // Composite: ${productId}:${sessionId}
+  sessionId: string;
+  productId: string;
+
+  level: LogLevel;
+  message: string;
+  messageHash?: string;
+
+  // Timestamps
+  timestamp: string;
+  receivedAt?: string;
+
+  // Source context
+  module: string;
+  file?: string;
+  line?: number;
+  function?: string;
+
+  // Thread/task context
+  threadId?: string;
+  correlationId?: string;
+
+  // Context (PII-scanned)
+  context: Record<string, unknown>;
+
+  // PII redaction metadata
+  redaction?: {
+    fieldsRedacted: string[];
+    patternsMatched: string[];
+  };
+}
+
+// ─────────────────────────────────────────────────────────────────────────────
+// DebugScreenshotDoc (metadata only)
+// ─────────────────────────────────────────────────────────────────────────────
+
+export interface DebugScreenshotDoc {
+  id: string;
+  sessionId: string;
+  productId: string;
+
+  // Blob storage reference
+  blobUrl: string;
+  blobPath: string;
+  containerName: string;
+
+  // Metadata
+  capturedAt: string;
+  trigger: ScreenshotTrigger;
+
+  // Dimensions
+  width: number;
+  height: number;
+  format: 'png' | 'jpeg' | 'webp';
+  sizeBytes: number;
+
+  // Privacy
+  sensitiveViewsBlurred: boolean;
+  blurRegions?: Array<{ x: number; y: number; w: number; h: number }>;
+
+  // Context
+  screenName?: string;
+  breadcrumbAtCapture?: string;
+}
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Input Schemas
+// ─────────────────────────────────────────────────────────────────────────────
+
+export const CreateDebugSessionSchema = z.object({
+  productId: z.string().min(1),
+  targetUserId: z.string().optional(),
+  targetAnonymousId: z.string().optional(),
+  targetDeviceId: z.string().optional(),
+  targetSessionId: z.string().optional(),
+  collectionLevel: CollectionLevelEnum.default('debug'),
+  captureLogs: z.boolean().default(true),
+  captureNetwork: z.boolean().default(true),
+  captureScreenshots: z.boolean().default(false),
+  screenshotOnError: z.boolean().default(true),
+  maxDurationMinutes: z.number().min(5).max(1440).default(60),
+});
+
+export const UpdateDebugSessionSchema = z.object({
+  status: SessionStatusEnum.optional(),
+  collectionLevel: CollectionLevelEnum.optional(),
+  captureLogs: z.boolean().optional(),
+  captureNetwork: z.boolean().optional(),
+  captureScreenshots: z.boolean().optional(),
+  screenshotOnError: z.boolean().optional(),
+  maxDurationMinutes: z.number().min(5).max(1440).optional(),
+});
+
+export const ListDebugSessionsQuerySchema = z.object({
+  productId: z.string().optional(),
+  status: SessionStatusEnum.optional(),
+  targetUserId: z.string().optional(),
+  from: z.string().datetime().optional(),
+  to: z.string().datetime().optional(),
+  limit: z.coerce.number().min(1).max(100).default(20),
+  offset: z.coerce.number().min(0).default(0),
+});
+
+export const IngestTracesSchema = z.object({
+  sessionId: z.string().min(1),
+  traces: z
+    .array(
+      z.object({
+        traceId: z.string().min(1),
+        spanId: z.string().min(1),
+        parentId: z.string().optional(),
+        name: z.string().min(1),
+        kind: SpanKindEnum.optional(),
+        startTime: z.string().datetime(),
+        endTime: z.string().datetime().optional(),
+        durationMs: z.number().optional(),
+        attributes: z.record(z.unknown()).default({}),
+        status: SpanStatusEnum,
+        statusMessage: z.string().optional(),
+        events: z
+          .array(
+            z.object({
+              name: z.string(),
+              timestamp: z.string().datetime(),
+              attributes: z.record(z.unknown()).optional(),
+            })
+          )
+          .optional(),
+        links: z
+          .array(
+            z.object({
+              traceId: z.string(),
+              spanId: z.string(),
+              attributes: z.record(z.unknown()).optional(),
+            })
+          )
+          .optional(),
+      })
+    )
+    .min(1)
+    .max(50),
+});
+
+export const IngestLogsSchema = z.object({
+  sessionId: z.string().min(1),
+  logs: z
+    .array(
+      z.object({
+        level: LogLevelEnum,
+        message: z.string().max(4096),
+        timestamp: z.string().datetime(),
+        module: z.string().min(1),
+        file: z.string().optional(),
+        line: z.number().optional(),
+        function: z.string().optional(),
+        threadId: z.string().optional(),
+        correlationId: z.string().optional(),
+        context: z.record(z.unknown()).default({}),
+      })
+    )
+    .min(1)
+    .max(50),
+});
+
+export const CreateScreenshotMetadataSchema = z.object({
+  sessionId: z.string().min(1),
+  capturedAt: z.string().datetime(),
+  trigger: ScreenshotTriggerEnum,
+  width: z.number().positive(),
+  height: z.number().positive(),
+  format: z.enum(['png', 'jpeg', 'webp']),
+  sizeBytes: z.number().positive(),
+  sensitiveViewsBlurred: z.boolean(),
+  blurRegions: z
+    .array(z.object({ x: z.number(), y: z.number(), w: z.number(), h: z.number() }))
+    .optional(),
+  screenName: z.string().optional(),
+  breadcrumbAtCapture: z.string().optional(),
+});
+
+export const QueryTracesSchema = z.object({
+  limit: z.coerce.number().min(1).max(200).default(50),
+  continuationToken: z.string().optional(),
+});
+
+export const QueryLogsSchema = z.object({
+  level: LogLevelEnum.optional(),
+  from: z.string().datetime().optional(),
+  to: z.string().datetime().optional(),
+  search: z.string().max(256).optional(),
+  limit: z.coerce.number().min(1).max(200).default(50),
+  continuationToken: z.string().optional(),
+});
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Inferred Types
+// ─────────────────────────────────────────────────────────────────────────────
+
+export type CreateDebugSessionInput = z.infer<typeof CreateDebugSessionSchema>;
+export type UpdateDebugSessionInput = z.infer<typeof UpdateDebugSessionSchema>;
+export type ListDebugSessionsQuery = z.infer<typeof ListDebugSessionsQuerySchema>;
+export type IngestTracesInput = z.infer<typeof IngestTracesSchema>;
+export type IngestLogsInput = z.infer<typeof IngestLogsSchema>;
+export type CreateScreenshotMetadataInput = z.infer<typeof CreateScreenshotMetadataSchema>;
+export type QueryTracesInput = z.infer<typeof QueryTracesSchema>;
+export type QueryLogsInput = z.infer<typeof QueryLogsSchema>;
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Event Bus Event Types
+// ─────────────────────────────────────────────────────────────────────────────
+
+export interface DiagnosticsSessionCreatedEvent {
+  sessionId: string;
+  productId: string;
+  targetUserId?: string;
+  createdBy: string;
+}
+
+export interface DiagnosticsSessionUpdatedEvent {
+  sessionId: string;
+  productId: string;
+  changes: Partial<DebugSessionDoc>;
+  updatedBy: string;
+}
+
+export interface DiagnosticsSessionCancelledEvent {
+  sessionId: string;
+  productId: string;
+  reason?: string;
+  cancelledBy: string;
+}
+
+export interface DiagnosticsSessionCompletedEvent {
+  sessionId: string;
+  productId: string;
+  stats: {
+    logCount: number;
+    traceCount: number;
+    screenshotCount: number;
+  };
+  endedAt: string;
+}
+
+export interface DiagnosticsIngestFatalEvent {
+  sessionId: string;
+  productId: string;
+  logEntry: DebugLogEntryDoc;
+  timestamp: string;
+}